Conventionally, in a production site, it has been necessary for an operator to perform an input operation into an information system to obtain the information of what operation has been performed by the operator and where the operation has been performed. To reduce such a burden, methods are being investigated to collect the information automatically by using a transmitter and a receiver that is capable of receiving a signal from the transmitter.
However, when the methods are used in a production site having many disturbances, etc., it is difficult for the receiver to receive the signal accurately.